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April 6, 2015
Using a Coolant Containing Lithium to Remove Heat from Plasma: Developing a Coolant Circulation Loop that Simulates the Fusion Power Generation System

In the future fusion energy generation we will remove heat from high-temperature hydrogen plasma and generate energy through a steam turbine. The mechanism for power generation with steam turbine is the same as that for thermal power generation. However, we cannot directly remove heat from the plasma itself. Rather, at the wall we stop the movement of high-energy particles generated by a fusion reaction, and after converting the kinetic energy of the particles to heat we then remove that heat. For that purpose, we have installed a wall that is one meter thick near the plasma for the purpose of capturing high-energy particles. We call this wall a “blanket” for covering plasma. In order to remove heat from the blanket to the outside, it is necessary to flow gas or liquid coolant inside the blanket and then remove the heat to the outside through a pipe. That is, the flow of the coolant material carries the heat to the outside. Through the heat so removed, we use a heat exchanger to boil water and then use that steam to power the generator’s turbine.

A prospective coolant material is liquid containing lithium. Considering that the temperature at which it becomes liquid is low, it does not react with air, and various other characteristics, molten salt (composed of metals such as lithium, sodium, and potassium, and a fluorine compound (salt); FLiNaK and others) and lithium lead alloys are the leading candidates. The fundamental characteristics of these materials is gradually becoming clearer through research. When considered for use in the magnetic field confinement fusion generation system, it will be necessary to test these materials flowing at high speeds inside a strong magnetic field. The flow of liquid imparts great influence upon the removal of heat, but how that flow will change inside a strong magnetic field is still not yet well understood. In order to conduct various tests in an environment even closer to an actual fusion energy system, we have developed a new testing device called the “Heat and Material Flow Loop Orosh2i-2.” This device has two loops that can circulate fluoride molten salt and lithium lead separately and a superconducting magnet that generates as much as 30,000 gauss, and among similar test devices it boasts performance at the highest level in the world. Moreover, this device is designated for joint research use by researchers in Japan and around the world. Making effective use of this new device, we are contributing to the early realization of the future fusion energy.